As electronic books and electronic textbooks become popular, learners have been able to employ a new learning method in which they understand the content of the electronic books and textbooks not only by eyes but also by ears using a speech synthesis technology. There is a great advantage to understanding the content of electronic books and electronic textbooks by ears. For example, a learning method for memorizing text while listing to the text repeatedly is called speech learning and it is known that the learning method improves learning efficiency. In this method, however, reading of synthesized speech is monotonous and thus it is hard to understand what is important. To prevent this, there is a technique of generating well-modulated synthesized speech using markup language called speech synthesis markup language (SSML).